Scientists are already 3D printing different kinds of tissue, from skin to livers, and someday they say it will be commonplace to simply print out a body part when needed.

NEW YORK -- Sixty years from now, we'll look back on today's 3D-printed tissue and organ technology and think it's as primitive as the iron lung seems to us now.

Six decades out, replacing a liver or a kidney will likely be a routine procedure that involves harvesting some patients cells, growing them and then printing them across artificial scaffolding.

Dr. Anthony Atala, director of the Wake Forest Institute for Regenerative Medicine, spoke at the Inside 3D Printing Conference here about where the technology is today, and what hurdles it still must overcome.

The biggest hurdle is being able to 3D print supportive vascular structure so that tissue can receive the oxygen critical to its survival once it's implanted into a patient.

Today, scientists can replicate tissue in small amounts beginning with the simplest: flat human skin tissue. Researchers have been able to create tubular blood vessels, and even parts of hollow organs of the body, such as the bladder. But, it's the solid, hard organs, such as the liver and the kidney, that are more complex and require far more vascular support to recreate successfully.

"We're working very hard to make sure we get there someday," Atala said.

It's not as insurmountable a goal as it may seem. For one, scientists don't need to replicate an entire organ. In fact, up to 90% of an organ can fail before it seriously affects the health of a patient, Atala said.

"Imagine you're playing tennis one weekend and you get chest pains. You go and get an x-ray and they find 90% of you're your heart vessel is occluded. The fact is you never had chest pain when your heart vessel was 80% occluded," he said. "It's the same thing with kidneys. You don't get into kidney failure until about 90% of your kidney is gone. So you have to burn 90% of your reserve before you get in trouble."

The current strategy of bioengineers is to create enough tissue to boost an organ that's failing while not completely replacing it, Atala said

Typically, the maximum distance between tissue and the vascular structures that support them is 3mm. That means that for every 3mm of tissue, physicians will have to be able to construct capillaries to support them.

Today, 3D bioprinting constructs a series of tissue held up by artificial scaffolding, like the iron beams in a building. First a layer of scaffolding is laid down, and then a layer of cells is laid down on top of that.

In the past, scientists have had to separately create the scaffolding, and then coat it with the living cells. That not only takes longer to complete, but it also places the living cells in danger of dying before they can even be implanted.

3D printing allows the scaffolding and living tissue to be printed together.

In order to construct veins and capillaries, they first print out a tubular construct made of dis-solvable material; they then coat the outside of that tube with muscle cells and the inside with venous barrier cells. A heart valve can be constructed in the same way; first by using dis-solvable scaffolding followed by outer muscular cells and interior barrier cells.

Researchers at Wake Forest have even successfully laid down heart cells; the completed tissue then begins to beat.

"Liver structures we print today last 30 days. They secrete urea, albumin and they produce [stem] layers. We're reproducing embryonic development of the kidney," Atala said.

Scaling up that tissue production is the challenge today, Atala said.

3D printed faces and skulls

While printing actual tissue holds the key to someday replacing body parts, another promising area is 3D printed bones. Today, 3D printing is used to create structural support.

For example, if a patient has been in an accident and lost part of their skull, physicians can create an exact 3D virtual image of the patient's skull through CT scans and use it to print out a hard polymer section of the skull. But 3D printers have yet to tackle the printing of actual bone.

At best, 3D printers represent an evolutionary step toward more advanced cranialfacial reconstruction, according to Dr. Amir Dorafshar, co-director of the Facial Transplantation Program at Johns Hopkins University.

Still, 3D printing has advanced surgery by leaps and bounds.

Less than 10 years ago, cranialfacial surgeons would act as artists, spending hours in an operating room trying to put the jigsaw puzzle of a smashed or deformed skull back together.

Through the use of 3D imaging, surgeons can perform the surgery on a computer screen before entering the operating room, affording them an exact model to follow once the scalpel begins its cuts.

Amir said where 3D printing is also evolving craniofacial surgery in its ability to produce exact surgical guides that are placed over the section of a patient's head or face. The plastic guides allow surgeons to make their cuts without fear of mistakes.

"Today, the gold standard is still to take tissue and bone from another part of the patient's body and transplant it," Dorafshar said.

The revolution will be when physicians can print up a bioactive bone scaffolding that includes a vascular structure to supply the living bone with nutrients and oxygen. "Imagine one day when we can recreate vascularized bone," Dorafshar said.

"I can assure you people will look back on these technologies someday and say, "Boy, weren't these primitive," Atala said.